1. Field of the Invention
The present invention relates to a compound type expert system which is suitably applicable to a control system for optimization of a plant or an engine, a diagnostic device for a plant, an engine, a vehicle or a computer system, or a backup system for operation of a vehicle, computer equipments or domestic electric devices.
2. Description of the Related Art
An expert system operates with the use of a computer program based on a knowledge base of expert's knowledge in a specific field. Therefore, by using the expert system, even a non-professional can do works as good as an expert does, which increases the application of the expert system since it meets the requirements of upgrading the data-processing quality and decreasing the number of workers or operators.
However, in accodance with the related art expert system, the data of the knowledge base has to be written as definite information without fuzziness and contradiction. Also, it is difficult to write fuzzy information of human feelings such as "young" or "the color is a little thin" in the knowledge base. Accordingly, to make such a fuzzy and complicated decision or dudgement as human feelings, the data amount of the knowledge base becomes very enormous, which makes it difficult to maintain and tune the knowledge base data. This is because that the inference according to the related art expert system ignores the partial satisfaction of required conditions.
On the other hand, there is a fuzzy expert system to which the fuzzy theory is applied to quantify the fuzziness of language information. In accordance with the fuzzy expert system, since it is possible to use qualitative language data, the data amount of the knowledge base can be much reduced. Also, the system admits the partial satisfaction of conditions to make an inference and allows entry of contradictory data in appearece since the system makes a conciliated decision from a plurality of intermediate judgements.
However, in accordance with the inference algorithm of the expert system according to the related art, the final inference result obtained during the process of making the conciliated decision from a plurality of intermediate judgements gives only a qualitative analysis and can not be used as information in the subsequent data processing operation without additional information data of human judgement regarding the result.
For example, in the field of control technique, the information data requires a concrete definite value for control motion such as "set the temperature to be 45.degree. C." or "incline the robot arm by 30.degree. C.". In order to obtain such a concrete data, that is, to make the information not fuzzy, in the fuzzy expert system, a numerical data is calculated from the result of inference with the use of mathematical technique. However, as mentioned above, since the inference result is qualitative, it can not be determined whether the calculated value is reasonable or not.
It is to be noted that the expert system and the fuzzy expert system are disclosed in "Electronic Data Communication Handbook" edited by Electronic Data Communication Society, published by Ohm Co., 1988, Nikkei Electronics, Mar. 21, 1988, and Japanese Patent Application Laying Open (KOKAI) Nos. 63-123177 and 63-123124.